1. Field of the Invention
The present invention relates to an optical transducer for detecting the position of a member which is movable with respect to a fixed structure, comprising a shutter provided with a plurality of transparent regions spaced by opaque regions, and a light emitter associated with a plurality of photosensitive cells which are subdivided into at least two groups of cells to generate two corresponding electrical signals which are out of phase with each shutter and cells.
2. Description of the Prior Art
A transducer is known, wherein the individual photosensitive cells are of an area which is a fraction of the area of each transparent region of the shutter and are disposed diffusely in the area on which the beam of light emitted by the light source impinges for the purpose of eliminating the errors due to the lighting distortion caused by incorrect positioning of the light emitter and cells with respect to the shutter. In that transducer, the photosensitive cells which are divided into two groups are all of the same dimensions and are disposed in accordance with a grid of rows and columns wherein the rows are orthogonal to the longitudinal axis of the transparent regions of the shutter and the columns are parallel to those regions. In addition, the cells in a group are disposed with the columns out of phase and with rows that are alternate with respect to the cells of the other group, and the spacing between the columns of the cells of each group is constant and equal to the spacing between the transparent regions of the shutter.
However, such a method of arranging the photosensitive cells requires a very high degree of accuracy, in particular as regards the distance between the columns, which is to be strictly equal to the spacing between the transparent regions of the shutter if it is desired that the electrical signals generated by the individual groups of cells are precisely indicative of the position of the shutter relative to the light source and cells. That involves very small tolerances and thus difficulties in construction and high production costs.